Electrical counter chain type timing arrangements



Oct. 27, 1964 J. w. DE LlSLE NICHOLS ETAL 3,154,743

ELECTRICAL COUNTER CPAIN TYPE TIMING ARRANGEMENTS Filed Dec. 7, 1959 5 Sheets-Sheet 1 I -o|| -o|| -ol| -o|| -o|| k3! 2ET52 "35 -34 35' 'L [LL I'[ "L L,

1' "*7 24 i 50 l 29 T 25 D L L L L *3! o':2/ l e D ol q /5 FIG.I. INVENTORS JOHN WINFRITH DE LISLE NICHOLS ALEXANDER CAMPBELL MAC KELLAR Oct. 27, 1964 J. w. DE LISLE NICHOLS ETAL ,7

ELECTRICAL COUNTER CHAIN TYPE TIMING ARRANGEMENTS Filed Dec. 7, 1959 5 Sheets-Sheet 2 F G r' INV-ENTORS:

JOHN wmp'moz LIISLE NICHIOLS ALEXANDER CAMPBELL MAC K'ELLAR Oct. 27, 1964 J. w. DE LlSLE NICHOLS ETAL 3,

ELECTRICAL COUNTER CHAIN TYPE TIMING ARRANGEMENTS Filed Dec. 7, 1959 5 Sheets-Sheet 3 0! '0 I *Ol -Ol -Ol l l #6 Z: i 8 I /0 I l 'L L L L l L L J r F :13 -J 1} l l I r2 t-o 3 A F\G.3.

7'4 INVENTORS:

' JOHN WINFRITH DE LISLE NICHOLS ALEXANDER CAMPBELL MAC KELLAR 1964 J. w. DE LISLE NICHOLS ETAL 3, 3

ELECTRICAL COUNTER CHAIN TYPE TIMING ARRANGEMENTS Filed Dec. 7, 1959 5 Sheets-Sheet 4 FICA.

JOHNIWINFRITH DE'LISLE NICHOLS VINVIENTORS:

ALEXANDER CAMPBELL MAC KELI AR Oct. 27, 1964 .1. w. DE LISLE NICHOLS ETAL 3, 3

ELECTRICAL comma 0mm TYPE TIMING ARRANGEMENTS Filed Dec. 7, 1959 5 Sheets-Sheet 5 O l O l O l l O l INVENTORS:

United States Patent 3,154,743 ELECTRICAL COUNTER CHAIN TYPE Til /KING ARRANGEMENTS John Winfrith de Lisle Nichols, Altrincharn, and Alexander Campbell MacKellar, Lindfield, England, assignors to National Research Development Corporation, London, England, a British corporation Filed Dec. 7, 1959, Ser. No. 857,636 Claims priority, application Great Britain Dec. 9, 1958 13 Claims. (Cl. 328-48) This invention relates to electrical timing arrangements and more particularly to such arrangements for generating a cyclically repeating predetermined pattern of output signals.

One application of such arrangements is to control the flashing of a lamp carried in a beacon such as a marine buoy. This flashing usually consists of a recurrent group of flashes, a group comprising up to, say, four flashes. It is also usually a requirement for such application that the ratio of lamp energisation time to cycle time, hereinafter referred to as the light duty cycle, should be maintained at a predetermined value.

An advantage of such a requirement is that in the case of battery-powered beacons a substantially accurate prediction can be made for replacement of batteries.

One object of the present invention is to provide a timing arrangement suitable for flashing-buoy control wherein the number of flashes in a group can readily be altered without afiecting the desired light duty cycle.

Accordingly there is provided electrical timing apparatus comprising a counter chain having first and second counter sections, the lowest order of the second counter section being higher than the highest order of the first counter section, a bistable two-state device having an ON' state and an OFF state, setting means for setting the counter chain to a predetermined condition and said twostate device to the ON state, means responsive to a selected condition or" said first counter section for triggering said two-state device to the (EFF state, and means responsive to a selected condition of said second counter section for operating said setting means to restore said counter chain to said predetermined condition and to set said two-state device to the ON state.

A further application of the present invention is to the monitoring of coded signals comprising a succession of first periods of signal transmissions separated by second periods of no signal transmission. A particular such application is to the monitoring of coded marine radio beacons providing a code in which said first periods are restricted to a maximum duration and said second periods are also restricted but to a maximum duration of different value.

.Thus, there is further provided by the present invention a modification of the above electrical timing apparatus wherein said setting means is operative to set only the counter chain to said predetermined condition, and comprising separate means for setting the two-state device to the ON state in response to a selected condition of either or both of said counter sections.

In order that the present invention may be clearl understood and readily carried into effect, particular embodiments thereof will now be described by way of example with reference to the accompanying drawings, in which:

FIGURE 1 illustrates one form of a timing arrangement suitable for control of a flashing buoy and meeting the requirements set out above, and

FIGURE 2 shows electrical waveforms i lustrative of the operation of the arrangement of FEGURE 1,

FIGURE 3 illustrates a modification of the apparatus of FIGURE 1 suitable for monitoring coded radio beacon signals,

FIGURE 4 shows electrical waveforms explanatory of the operation of the apparatus by FIGURE 3, and

FIGURE 5 illustrates the apparatus of FIGURES 1 and 3 in composite form.

In FIGURE 1 block 1 represents a conventional freerunning multivibrator and blocks 2 to 5 represent twostate devices connected in cascade together with block 1 to form a five-stage binary counter. The blocks 1 to 5 each comprise sections marked 0 and 1 to indicate the two operating conditions and the expressions 0 signals and 1 signal are used hereinafter to denote an active output signal from the appropriate counter stage when it is in the 0 or 1 condition respectively.

Waveforms (a) to (e) of FIGURE 2 illustrate the output waveforms of the 0 sections of counter stages 1 to 5 respectively during a complete cycle of the counter from 00000 to 11111, after which the counter automatically recycles.

Diodes 6 to 10 are connected between the 0 sections of stages 1 to 5 respectively and a common input lead to an amplifier 11. These diodes are arranged so that the common input lead to amplifier 11 is clamped to a negative potential source until all of counter-stages 1 to 5 are in the 0 condition. The last counter-stage to assume this condition removes the clamped condition and provides an input pulse to amplifier 11. Thus amplifier 11 generates an active output signal only during the condition 09000 of the counter.

The active output signal from amplifier 11 is employed to trigger a bi-stable element 12 to the 0 condition and the 0 signal therefrom opens a gate 13.

The 0 signal from stage 1 of the counter is applied to gate 13 and will be passed if the gate has been opened by the action of a 0 signal from element 12. Thus, active output signals are passed by the gate 13 during even counts of the counter, that is, when stage 1 is in the 0 condition, and in the present caseare amplified by a power amplifier 14 and then employed to fiash a lamp 15.

A selector switch 16 comprising three diodes 17, 18 and 19 has conections to a first section of the counter consisting of stages I, 2 and 3. These diodes may be connected via individual ganged-switching.members 2t 21 and 22 to open-circuited, or continuous flash contacts, as shown, or to one of four other contact positions. Considering these four. positions in clockwise sequence from the continuous flash contact, it will be seen that the connections to counter stages 1, 2 and 3 of the counter are such that the diodes 17, 18 and 19 will all be nonconductive only for the conditions 010, O01, 011 and 000 of stages 1, 2 and 3. Diodes 1'7, 18 and 19 are connected to a common input lead to an amplifier 23 whereby amplifier 23 only generates an output signal in response to non-conductive conditions for all of diodes 17, 13 and 19.

The output signals from amplifier 23 are applied to trigger bi-stable element 12 to the 1 on-condition thereby closing gate 13. Thus, dependent on the setting of selector switch 16, the lamp 15 will be flashed once, twice, three or four times in a cycle before the gate 13 is closed.

It will be seen that if the counter is allowed to execute complete cycles of thirty-two counts, then the respective light dutycycles for the latter group flashes are 1:32, 2:32, 3:32 and 4:32.

A further selector switch 24 comprising three diodes 25, 26 and 27, having connections to a second section or the counter consisting of stages 4 and 5, may be switched to an open-circuited continuous flash contact, three contacts connected individually 'to the diodes 25, 26 and 27, or a further open-circuited contact, in synchronism with switching of the selector switch 16 to its continuous flash contact position or other four positions respectively.

The diodes 25 and 27 are connected to the 1 section 3 of stage 4, the diode 26 is connected to the 1 section of stage 5, and the diode 27 is also connected via a resistor 28 to the section of stage 5. The switching member' 29 of switch 24 is connected to an amplifier 30, the output signal from which is applied via five diodes 31 to 35 to the 0 sections of counter stages 1 to respectively.

The latter arrangement is such that when the counter reaches the condition 00010, 00001 and 00011 respectively, then, dependent on which of the associated contacts'the switching member 29 is connected to, so the amplifier 30 generates an output signal at the appropriate counter condition, which signal is applied via blocking diodes 31 to 35 to set the counter to the 00000 condition.

The further open-circuited contact of switch 24 provides no output signal for recycling since automatic recycling'occurs at the correct time for the case of four flashes to a group.

Waveforms (f) to (i) and (j) to (m) of FIGURE 2 illustrates the "0 signal outputs from bi-stable element 12 and the output signals derived from the gate 13 respectively for the four operative positions of the selector switches 16 and 24, the latter waveforms also illustrating the resultant sequence of lamp flashes. It will be noted that the light duty cycle in the respective cases are 1:8, 2:16, 3:24 and 4:32, that is, they are maintained constant at 1:8.

In FIGURE 2 the on-condition of waveforms (a). to (i) is the lower level and for waveforms (j) to (m) the higher level is the on-condition. Furthermore, in waveforms (f) to (m) the symbol R denotes recycling to the counter condition 00000.

For the present case of application to marine buoys it is usual for the required light duty cycle to be 1: 10. This is achieved by suitable choice of the :multivibrator mark/ space ratio. Since, as pointed out above, the light duty cycle of the above arrangement is constant it is necessary 'only to consider the case in which a group consists of one flash. If the multivibrator (block 1 of FIGURE 1) mark/ space ratio is p:q, then the light duty cycle is p:4(p-|-q). This is required to be 1:10 so that an .integral solution of 10p=4p+4q will give the necessary multivibrator mark/ space ratio. The lowest integral solution is clearly p=2, q=3. Thus, by making the multivibrator mark/space ratio 2:3 a constant light duty cycle of 1:10 is attained in the above-described arrangement.

Clearly other ratios may be readily attained by suitable adjustment of the multivibrator mark/space ratio. The capacity of the two counter sections is determined primarily by the maximum number of output signals required in one group. However, if the light duty cycle requires a multivibrator mark/ space ratio such that p q, it may be simpler to have more than the minimum number of counter stages. Thus, in the above example, where a maximum of four flashes is required, the minimum capacity of the first counter section is eight counts, but if the desired light duty cycle is in excess of 1:16, it may be simpler to have a first counter section capacity of sixteen counts, for example. In practice it is preferable to construct the circuit arrangements so that where possible circuit elements are consuming more power when they are active than when they are inactive. This is particularly so where application to marine buoys is required in which case the power sources are limited. However, other things being equal it is desirable in any event that circuit arrangements be used which are as economical in power requirements as possible.

Afurther application of the invention is to the monitoring of time schedules in electrical apparatus and in one example it is proposed to construct monitoring apparatus for use with coded marine radiobeacons. Such beacons usually operate under the control of a clock pulse generator which provides timing pulses of short duration at regularly recurring intervals. The coded radio signals usually comprise signal pulses of predetermined period, referred to as marks, separated by periods of no signal transmission for different predetermined periods, referred to as spaces. 7

Correct operation of such a beacon'can be assumed providing that the following conditions are maintained:

(i) The clock pulse generator is operating. This is indicated by the presence of the timing pulses recurring at periods not greater than the allotted predetermined periods and (ii) During code transmission no space or mark exceeds its predetermined period.

It will be seen that these conditions do not ensure complete accuracy of operation but afford an indication of such a high probability of accurate operation as to be quite satisfactory for practical purposes.

FIGURE 3 illustrates one embodiment of monitoring apparatus according to the invention which is in effect a modification of the apparatus of FIGURE 1 and similar reference numerals are used where appropriate. For the sake of simplicity it will be assumed that it is required to monitor a coded radio beacon providing clock pulses every 16 seconds, and a code transmission comprising marks of 16 seconds duration and spaces of 4 seconds duration. Reference will also be made to the waveforms of FIGURE 4 which are explanatory of the operation of the apparatus of FIGURE 3.

I In FIGURE 3 blocks 1 to 5 represent a binary counter chain as before associated with diodes 6 to 10 which are also employed for resetting the counter in this case. The multivibrator stage in this case is required to operate with equal mark/space of 1 second each and FIGURE 4a represents the 0 section output of this stage.

The input to reset amplifier 30 is via a two-position relay contact CA2 one contact position of which is connected to a source of positive potential via a switch T1 and the other contact position of which is connected to a further two-position relay contact C2. The contact positions of C2 are connected via separate capacitors 50 and 51 to the intermediate point of a series-connection of a resistor 52 and a capacitor 53 between the positive potential source just mentioned and a negative potential source.

A connection is made from the 1 section of counter stage 3 via a first contact position of two two-position relay contacts Cl and CA1 to amplifier 11. A connection is also made to this amplifier from the 1 section of counter stage 5 via the second contact position of CA1. The second contact position of C1 is connected directly to that of CA1.

The output lead of amplifier 11 is connected to the ON input lead of bistable two-state device 12, the 0 section output of which is applied in this case to an alarm relay A. In operation the device 12 is normally in the 1 state, that is, OFF. The device 12 may be set to the OFF state initially or when required by means of a potential source applied via a manual switch T2 and amplifier 23. 7

To check the operation of the clock pulse generator in the beacon switch T3 is closed to operate relay CA/2 and set the two-position relay contacts CA1 and CA2 as shown. Two-position relay contacts C1 and C2 are also set to the positions shown by a relay 0/2 in its non-energized state with switch T4 open. Each occurrence of a timing pulse in the radio beacon is arranged to cause switch T1 to close temporarily so applying a positive pulse to reset the counter via contact CA2 and amplifier 30. This operation is represented by FIGURE 4(b). Thus the counter never reaches a count of 17 during correct timing pulse generation in the beacon. If there is a failure'in such generation as shown by FIGURE 4(0) repre: senting an excessive delay between successive timing pulses then the counter reaches a count of 17. At this time, stage 5 changes to' the 1 state, FIGURE 4(d) and an output pulse is applied via contact CA1 and amplifier 11 to device 67 switch two-state device 12 to the ON state and so operate alarm relay A. This is indicated by FIG- URE 4(e) During code transmission two position relay contacts CA1 and CA2 are set to the oher positions from those shown by opening switch T3 to de-energise relay CA/Z. Also switch T4 is closed and signals representing the code transmission, FIGURE 4(f), applied to relay C/2 to energise this relay during marks and to deenergise it during spaces. Thus, if the coded transmission is to meet the above condition (ii) contact C2 will change position within 4 seconds to dscharge capacitor 51 and reset the counter at the end of a space, and will return again within 16 seconds to discharge capacitor 50 to reset the counter once more. This normal operation is represented by FIGURE 4(g).

Clearly the values of resistor 52, capacitor 53 and the potential sources are required to be such that capacitors 50 and 51 become charged at least within the duration of a space.

In the event of an excessive space, FIGURE 4(h), the counter reaches a count of 5 and stage 3 changes to the 1 state, FIGURE 4(1'), producing an output pulse, FIGURE 4( j), which sets ofi alarm relay A via contacts C1, CA1, amplifier 11, and device 12.

Shnilarly, in the event of an excessive mark, FIGURE 4(k), the counter reaches a count of 17 and stage 5 changes to the 1 state, FIGURE 4(l), to produce an output pulse, FIGURE 4(m), which switches on the alarm relay A.

It will be seen that the pulses which switch on the alarm have been shown as equivalent to a count of one digit. This has been done since this would be the case if the selector switches 16 and 24 of FIGURE 1 were included in FIGURE 3 as shown in dotted outline to give a variety of space and mark periods which could be monitored. Also for simplicity marks and spaces have been shown as exactly 16 seconds and 4 seconds duration, respectively.

In one actual example of a coded marine radio beacon with which the monitoring aspect of the invention is to be associated the code transmissions include Morse code letter combinations comprising short marks, A second duration, representing dots and longer marks, /4 second duration, representing dashes. The marks of each individual letter are separated by short spaces, A second duration, and the individual letters themselves are separated by longer spaces, second duration. The letter combination will normally be repeated a few times after which a long mark, 25 seconds duration, is transmitted followed by a few more repetitions of the Morse code letter combination.

The letter combinations, and direction finding mark are Thus, the complete code transmission comprises three difierent marks and three different spaces and is satisfactorily monitored according to the invention by setting the monitor to operate its alarm at a time at least just greater than the'longest mark, that is the direction finding mark, and at a time at least just greater than the longest space, that is the space separating letter combinations and the latter direction finding mark, during monitoring a mark and a space respectively.

Also in practice the code timing schedule is derived from the clock pulses generated in the beacon so that during each 1 minute code transmission only code monitoring is required. It is only during the 5 minute periods between code transmissions that clock pulse generation is required to be monitored. Also the code/no code time schedule is derived from the clock pulses and it is proposed that for the above monitoring application of the invention the monitor is connected with the radio beacon control circuits whereby relays CA/Z and C/2 of FIG- URE 2, or equivalent components, are operated automatically in response to the latter time schedule.

FIGURE 5 illustrates the apparatus of FIGURES 1 and 3 in combined form as it may be produced in practice. The contacts of switch S would be set as shown for use as a coding apparatus with gate 13, amplifier 14, and lamp 15 connected as in FIGURE 1. For use as a monitoring apparatus switch contacts S would be set to the positions other than those shown and an flarm relay connected as shown in FIGURE 3. In this embodiment switches 16 and 24 are replaced by a composite switch and diode arrangement D5 of similar form from which pulses representing any count up to 32 may be selected.

The multi vibrator stage 1 would be provided with variable means to set its mark/ space ratio to a desired value such as 2:3 or 1:1 for the above examples, thus afiording greater flexibility of application. For this purpose it may be preferable to employ a separate multivibrator M driving the first counter stage as is in fact shown.

Clearly, the components of the above apparatus which are exclusive to one application of the apparatus, such as gate 13, amplifier 14, lamp 15 and alarm relay A, need not form a part of the basic equipment and can be appropriately connected dependent on the use to which the apparatus is to be put. Also the relays (3/2 and CA/Z together with their associated two-position contacts may be left out of the basic apparatus and connected into the circuit at appropriate terminals when application to monitoring is desired. Thus, the basic manufactured apparatus need only comprise the components above switch S, suitable terminal means being provided for connecting suitable ancillary equipment into the circuit.

It is proposed for the above examples to employ transistors and diodes for the sake of economy of space and power. However, any suitable conventional circuit arrangements may be employed.

Although the invention has been described by way of application to marine beacons, it is not intended to be limited thereby and may readily be applied where suitable to other uses, for example, to meet digital computer requirements.

We claim:

1. Electrical timing apparatus comprising a counter chain having first and second counter sections, the lowest order of the second counter section being higher than the highest order of the first counter section, a bistable twostate device having an ON state and an OFF state, setting means for setting the counter chain to a datum condition and said two-state device to the ON state, means responsive to a predetermined condition of said first counter section for triggering said two-state device to the OFF state, first selection means for selecting the predetermined condition of said first counter section, means responsive to a predetermined condition of said second counter section for operating said setting means to restore said counter chain to said datum condition and to set said two-state device to the ON state, second selection means for selecting the predetermined condition of said second counter chain, and means for operating said first selection means and said second selection means in unison to maintain constant the ONzOFF time ratio of said twostate device for diiferent values of combined ON and OFF times.

2. A modification of the apparatus of claim 1 wherein said setting means is operative only to set the counter chain to said datum condition, and comprising separate means for setting the two-state device to the ON state in response to a selected predetermined condition of either or both of said counter sections.

3. Apparatus according to claim 1 wherein said counter chain is a binary counter chain, a predetermined group of successive binary stages including that of least significance forming said first counter section and the remainder of said chain forming said second counter section, and comprising an output gate, means for applying to said output gate signals representing alternative states of the counter stage of least significance, means for opening said output gate .in .response to the ON state of said two-state device, and means for closing said output gate in response to the OFF state of said two-state device.

4. Apparatusiaccording to claim 2 comprising means for operating said :sett-ingmeans. in respopnse to the terminations of a succession of events to be monitored.

5. Apparatus according tolclaim 4 wherein said counter chain is a binary counter chain .a predetermined group .of successive binary stages including that of .least significance forming said first counter section and the re- 7 mainder of said chain forming said second counter section, and comprising utilisation means operative in response to the ON state of said two-state device.

6. Apparatus according to claim 4 comprising additional means for operating said setting means in response to a further event to be monitored and means for selec tively connecting this additional means .or said first-mentioned means for operating said setting means in response :to a succession of events to be monitored. a

7. .Electrical'timing apparatus comprising a counter chain having first and second countersections, the lowest order of thesecond counter section being higher than the highest order of the "first counter section, a bistable two-state device having an ON state and anti-FF state, setting means for setting the counter chain to a datum condition, means responsive to a predetermined condition of said firstcounter section for triggering said two-state device to the OFF state, means for selecting the predetermined condition of said first counter section, means responsive'to a predetermined condition of said second counter section for operating said setting means to restore said counter section to said datum condition, means for selecting the predetermined condition of said second counter section, additional means for operating said setting mean in response to the terminations of a succession of events to be monitored comprising two capacitors, means for charging said capacitors during a time less .than the duration of any event to be monitored, and means for discharging said capacitors alternately in .response to the terminations of successive one of said events, and separate setting .means for setting said twostate device to the ON state in response to a predetermined condition of either of said counter sections.

8. Electrical timing apparatus comprising a multi-stage binary counter chain, a bistable two-state device having an ON state and an OFF state, a utilization device, .a connection from the first stage, being the stage of least significance, in said counter chain to said utilization device, said connection including a gate circuit, a connection from said bistable device to said gate circuit operative to open said gate circuit for the passage of signals from said first stage to said utilization device when said bistable device is in .the ON state, connections from a plurality of the stages of said counter chain to first circuit selecting means, means for deriving from said first circuitselecting means a signal in response to a selected combination of states of the stages of said counter chain and'applying said signal to reverse said two-state device, connections from a dilferent plurality of the stages of said counter chain to second circuit selecting means, means for applying a signal from the circuit selected by said second circuit selecting means to all the stages of said counter chain 'to restore them to a datum condition and means for operating said first circuit selecting means and said second UNITED STATES PATENTS 2,493,627 7 Grosdofi Jan. 3, 1950 2,563,841 Jensen Aug. 14, 1951 2,970,763 Freeman Feb. 7, 1961 3,002,151 Broderick et al Sept. 26, 1961' 3,044,065 Barney et a1. 7 July 1 0, 1962 3,050,685 Stuart Aug. 21 1962 3,079,554 7 Ranky Feb. 26, 1963 v v FOREIGN PATENTS 704,816 Great Britain Mar. 3, 1954 S circuit selecting means in unison to maintain constant the ON:OFF time ratio of said bistable device for ditierent values of combined ON and'OFF times.

9. Apparatus as claimed in claim 8 including means responsive to the restoration of the stages of said counter chain to said datum condition for setting saidtwo-state device to the ON state.

' 10. Electrical timing apparatus comprising a multistage binary counter chain, a bistable two-state device having an ON state and an OFF state, a utilisation device, a connection from the first stage being the stage of least significance in said counter chain to said utilisation device, said connection including agate circuit, a connectiontrom said bistable device to said gate circuit operative to open said gate circuit for the passage of signals from said first stage to said utilisation device when said bistable device is in the ON state, connections from a plurality of the stages of said counter chain to first circuit selecting means, means for deriving from said first circuit selecting means a signal in response to -a selected combination of states of the stages of said counter chain and applying said signal to reverse said two-state device, connections from a difierent plurality of the stages of said counter chain to second circuit selecting means, means for deriving from said second circuit selecting means a signal in response to a selected combination of states of the stages of said counter chain and applying said signal to all the stages of said counter chain to restore them to a datum condition, alternative resetting means for supplying a signal periodically to restorethe stages of said counter chain to their datum condition, means responsive to a predetermined condition of said counter chain for reversing said two- 'state device into the ON state and indicator means connected to said two-state device to indicate said reversal whereby operation of said indicator means occurs only when the periodic operation of the alternative resetting means is delayed beyond the time within which said pre-. determined condition of said counter chain is reached.

11. Apparatus as claimed in claim 10 including circuit selecting means for selecting the predetermined condition of said counter chain.

12. Apparatus as claimed in claim 11 including changeover switching meansconnected to select for operation either the first named means for restoring the stages of said counter chain to their datum condition and said utilization device or the alternative means for restoring the stages of said counter chain to their datum condition and said indicator means. i

13. Apparatus as claimed in claim 10 including means for operating said first circuit selecting means and said second circuit selecting means in unison to maintain constant the ONzOFF time ratio of said bistable device for different values of combined ON and OFF times.

References Cited in the file of this patent 

1. ELECTRICAL TIMING APPARATUS COMPRISING A COUNTER CHAIN HAVING FIRST AND SECOND COUNTER SECTIONS, THE LOWEST ORDER OF THE SECOND COUNTER SECTION BEING HIGHER THAN THE HIGHEST ORDER OF THE FIRST COUNTER SECTION, A BISTABLE TWOSTATE DEVICE HAVING AN ON STATE AND AN OFF STATE, SETTING MEANS FOR SETTING THE COUNTER CHAIN TO A DATUM CONDITION AND SAID TWO-STATE DEVICE TO THE ON STATE, MEANS RESPONSIVE TO A PREDETERMINED CONDITION OF SAID FIRST COUNTER SECTION FOR TRIGGERING SAID TWO-STATE DEVICE TO THE OFF STATE, FIRST SELECTION MEANS FOR SELECTING THE PREDETERMINED CONDITION OF SAID FIRST COUNTER SECTION, MEANS RESPONSIVE TO A PREDETERMINED CONDITION OF SAID SECOND COUNTER SECTION FOR OPERATING SAID SETTING MEANS TO RESTORE SAID COUNTER CHAIN TO SAID DATUM CONDITION AND TO SET SAID TWO-STATE DEVICE TO THE ON STATE, SECOND SELECTION MEANS FOR SELECTING THE PREDETERMINED CONDITION OF SAID SECOND COUNTER CHAIN, AND MEANS FOR OPERATING SAID FIRST SELECTION MEANS AND SAID SECOND SELECTION MEANS IN UNISON TO MAINTAIN CONSTANT THE ON: OFF TIME RATIO OF SAID TWOSTATE DEVICE FOR DIFFERENT VALUES OF COMBINED ON AND OFF TIMES. 